1. Field of the Invention
The present invention generally relates to an analysis method for turbine-generator torsional vibrations and, more particularly, to an analysis method for turbine-generator torsional vibrations due to power transmission system.
2. Description of the Related Art
Presently, the power transmission structure of Taiwan is mainly distributed at the west coast of Taiwan like a narrow belt, which is briefly divided into “North part,” “Center part” and “South part” connected by transmission lines with a high voltage level of 345 kV, and a sketch of the pylon, arrangement of conductors and voltage-time diagram of the used three-phase power transmission system are shown in FIGS. 1a, 1b and 1c. Owing to the increasing population of the west coast, it is hard to obtain sufficient and suitable lands for pylons and substations for any new transmission line. On the other hand, power transmission for transmitting electrical power from the “South part” and “Center part” to the “North part” is truly important for the Taiwan power transmission structure since the population of the north part in Taiwan is much higher than those of the other parts. However, the above fact results in a high loading of the power transmission lines, a large rotor angle difference between north and south parts of Taiwan power plants, and worse stability of power supply. Therefore, how to increase the capacity of a power transmission system has become an important issue in this field.
Please refer to FIGS. 2a, 2b and 2c, which are a sketch of the pylons, arrangement of conductors and voltage-time diagram of a four-phase power transmission system. Adjusting the used three-phase power transmission system to a four-phase power transmission system may actually improve the capacity of power transmission lines because a four-phase power transmission system has properties such as high transient stability, low interference induced by electromagnetic filed, and reduced conductor arrangement in space. Besides, the four-phase power transmission system is a power transmission system with even number of phases and similar to the conventional three-phase power transmission system. Therefore, the four-phase power transmission system may be an acceptable solution for the situation in Taiwan.
However, most of the studies of a four-phase power transmission system are focused on transformation technique, differential protection from a three-phase power transmission system to a four-phase power transmission system, and economic analysis, and none of them is about interaction effects on connected turbine-generator and four-phase power transmission system.
Moreover, in order to acquire a low cost in power generation and high thermal efficiency, the scales of power generators are gradually increased because nuclear power generations were introduced to Taiwan. However, once the scales of power generators are increased, transient fault accident of the power transmission system can easily result in torsional vibrations of fan wheel and rotor shaft of the turbine-generator and lead to fatigue life expenditure problems on the fan wheel and rotor shaft.
Accordingly, it is necessary to analyze the affection of torsional vibrations to the turbine-generator caused by transient fault of the power transmission system prior to actually applying the four-phase power transmission system to the power transmission structure of Taiwan. Thus, an analysis method for turbine-generator torsional vibrations affected by power transmission system is required to examine the feasibility and effectiveness of a four-phase power transmission system.